"Canon" piano version of Pachelbel (gentle and slightly sad)

"Tears" The Daydream (sad)

"Kiss The Rain" The imprint of "Yiruma (beautiful)"

"Bird Poetry" piano version (the second version meets your requirements very well)

"Castle in the Sky" piano version

"Paganini Grand Fantasy Bell" Liszt (high difficulty, very good)

"Paganini Transcendental Etude" Liszt (based on Paganini's 24 Caprices

"Hungarian Rhapsody" Liszt (Awesome Rhapsody)

"Etude in E major Farewell" Chopin (Farewell but not sad)

"Fantasy Impromptu in C sharp minor" Chopin (one of Chopin's most frequently performed improvisations)

"Puppy Waltz" Chopin (flexible and cute)

"Revolution Etude "Chopin (it has a very shocking feeling in the second part, and it meets your requirements)

"Pathétique 2nd Movement" Beethoven (a nice piece)

" "For Alice" Beethoven

"Wanderer Piano Fantasy in C Major" Schubert